Organic electroluminescence devices have drawn the broad attention of people due to the advantages such as thin bodies, large planar sizes, complete fixation and good flexibility, and organic white electroluminescence devices have become a research hotspot because of the great potential in solid state illumination light source and liquid crystal backlight light source.
As early as in 1950s, Bernanose. A et al began the research on organic electroluminescence devices (OLED). The initial research material was anthracene single crystal wafer. Because of the problem of the large thickness of the single crystal wafer, the required driving voltage was very high. In 1987, C. W. Tang and Vanslyke of Eastman Kodak Company of the USA reported the organic small molecule electroluminescence device of the structure of ITO/Diamine/Alq3/Mg:Ag, whose brightness under the working voltage of 10 volts reached 1000 cd/m2, and external quantum efficiency reached 1.0%. The research on electroluminescence raises the concern of scientists, and people see the possibility of the application of organic electroluminescence devices in displaying, which initiates the research and industrialization of organic electroluminescence devices. The organic luminescence material system comprises the fluorescence system and the phosphorescence luminescence system, of which the fluorescence system only utilizes the singlet state exciton energy, while the phosphorescence system can additionally utilize the triplet state exciton energy.
In traditional organic electroluminescence devices (OLED) that employ phosphorescent dyes as the luminescent layer, because the life of the triplet state excitons is longer than the life of the singlet state excitons, the transfer distance of the triplet state excitons is longer than the transfer distance of the singlet state excitons (NATURE, Vol 440, 13 Apr. 2006). The triplet state excitons entering the transport layer will cause energy loss. In general, in order to confine the triplet state excitons within the luminescent layer, it is required to design barrier layer structures on both sides of the luminescent layer (film. Phys. Rev. B 66, 14422-14428 (1999)). Additionally, barrier layers are provided in N-doped OLED electron transport layer structures, to prevent N dopants from entering the luminescent layer to result in exciton quenching, but the adding of the barrier layers will complicate the device structure.
The above methods of adding barrier layers between the phosphorescence luminescent layer and the transport layer restrict excitons entering the transport layer and block the migrating of N dopants to the luminescent layer to a certain extent, but result in the complication of the device structure.